Eddy current flaw detector utilizing a field coil and pick-up coils in approximatelyparallel relation to the test piece with the pick-up coils located within the field coil

Claim 1

APPARATUS FOR FLAW TESTING WORKPIECES OF ELECTRICALLY CONDUCTIVE MEATERIAL COMPRISING: A. GUIDE MEANS DEFINING A FEED PATH FOR SAID WORKPIECE THROUGH A DETECTOR STATION, B. A DETECTOR HEAD AT SAID STATION INCLUDING (I) A FIELD COIL HAVING AN END FACE ARRANGED IN CLOSELY SPACED AT LEAST APPROXIMATELY PARALLEL RELATION TO THE SURFACE OF SAID WORKPIECE TO OVERLIE AN ELEMENTAL AREA OF SAID SURFACE, (II) AT LEAST A PAIR A PICK-UP COILS HAVING END FACES ALSO ARRANGED IN CLOSELY SPACED AT LEAST APPROXIMATELY PARALLEL RELATION TO SAID SURFACE AND EACH OF A SMALLER AREA THAN THE FIELD COIL, AND DISPOSED WITHIN IT AS VIEWED NORMAL TO SAID SURFACE, IN RESPECTIVE POSITIONS SPEED FROM EACH OTHER IN A PREDETERMINED DIRECTION TO OVERLIE DIFFERENT PORTIONS OF SAID ELEMENTAL AREA, SAID PICK-UP COILS BEING CONNECTED IN OPPOSITION, (II) SAID FILED COIL AND SAID PICK-UP COIL END FACES BEING SUBSTANTIALLY THE SAME DISTANCE FROM SAID SURFACE, C. A SOURCE OF HIGH FREQUENCY ALTERNATING ELECTRIC CURRENT FORMING A CARRIER, SAID SOUCE BEING CONNECTED WITH SAID FIELD COIL TO SET UP AN ALTERNATING MAGNETIC FIELD IN A SURFACE LAYER OF SAID WORKPIECE AT SAID SURFACE THEREOF AND AT SAID DETECTIONG STATION TO INDUCE A PREDETERMINED EDDY CURRENT PATTEN IN CIRCUITS AFFORDED BY THIS LAYER IN SAID ELEMENTAL AREA, WHEREBY VOLTAGES ARE INDUCED IN SAID PICK-UP COILS OF A MAGNITUDE AND PHASE DEPENDENT ON SAID EDDY CURRENT PATTERN, D. MECHANICAL MEANS FOR EFFECTING RELATIVE SCANNING MOVEMENT IN SAID PREDETERMINED DIRECTION BETWEEN SAID WORK-PIECE ON THE ONE HAND AND SAID DETECTOR HEAD ON THE OTHER HAND TO CASE SAID WORKPIECE TO MOVE PAST SAID FIELD COIL AND SAID PICK-UP COILS WITHINOUT MOVEMENT THROUGH THEM, E. SAID FIELD COIL AND SAID PICK-UP COILS HAVING INDUCTIVE COUPLING WITH SAID CIRCUITS IN SAID SURFACE LAYER OF THW WORKPIECED THROUGH A MAGNETIC FIELD PATH, SAID PATH CONTAINING ONLY NON-MAGNETIC AND ELECTRICALLY NON-CONDUCTIVE MATERIAL, F. INDICATOR MEANS CONNECTED WITH SAID PICK-UP COILS AND INCLUDING AMPLIFIER MEANS AND DE-MODULATOR MEANS FOR SEPARATING FROM SAID CARRIER A MODULATION COMPONENT OF ALTERNATING VOLTAGES INDUCED IN SAID PICK-UP COILS RESPECTIVELY AND PRODUCED IN RESPONSE TO SAID RELATIVE MOVEMENT WHENEVER A FLAW IN SAID SURFACE LAYER PASSES SAID FIELD COIL AND PICK-UP COILS.